The invention relates generally to the area of gas expansion related engines and more particular to a constant combustion, constant volume rotary engine.
The design of small engines for the automotive industry has been diligently pursued for a century and in spite of many ingenious alternatives offered, the overwhelming majority of automobile engines made are of the four-cycle reciprocating piston variety, as originally proposed by Otto, Lanchester, and Diesel.
Since 1947, gas turbine drives have been often proposed and several vehicles have been demonstrated, ranging from off-highway dump trucks to high-speed passenger cars. None have been commercially viable to the point where volume production could be undertaken at the rates common to the gasoline reciprocating engine or the diesel engine, which is now becoming increasingly competitive.
Rotary engines have been introduced, typified by the Wankel rotating combustion engine, and over half a million engines have been manufactured over the past ten years. Problems of high fuel consumption and exhaust emission remain to be solved, although the engine is attractive from the standpoint of lower bulk and freedom from vibration.
Each type of engine has certain advantages over its competitors, and a desirable goal for a new engine would be to combine the best features of each. Certain attributes result from millions of hours of developmental and service experience under every climate and condition of duty. Other attributes arise from increasing sophistication and discernment of the users. Yet others come from the political and legislative environmental and economical concerns.
As the finiteness of liquid hydrocarbon fuel supplies becomes daily more apparent, the attention of the public to the need for more efficient use of the available supply has been focused and continues to drive the search for newer and better engines.
The following features are sought in general:
low first cost PA1 low maintenance cost PA1 low vibration and noise PA1 best fuel economy PA1 low emissions PA1 low bulk and weight PA1 fast response PA1 easy starting PA1 highest possible temperature of combustion PA1 shortest fuel burning time PA1 completeness of combustion before expansion PA1 lowest radiation and conductive/convective heat loss to external heat sink PA1 lowest exhaust gas temperature following from maximum extraction of mechanical work during the expansion process PA1 highest strength/density ratio for minimum material cost PA1 lowest use of exotic or rare alloying elements PA1 high internal damping coefficient for parts subject to vibration PA1 longest fatigue/wear life for parts subject to flexure or abrasion
Thermodynamic considerations for most efficient use of the liquid fuel linclude:
Mechanical considerations for most efficient use of the materials of construction include:
Conventional 2-cycle or 4-cycle reciprocating or rotary engines utilize intermittent or cyclic combustion processes to permit use of extremely high temperatures and pressures over a small portion of the cycle, giving a lower average cycle temperature suitable for low-cost materials such as aluminum or cast iron. The combustion temperature may exceed 3000.degree. F. instantaneously, but the average piston temperature is lower than 500.degree. F. as heat is conducted away by coolants, lubricants, and the incoming charge air.
Gas turbines employ constant volume combustion and continuous burning within a combustion chamber supplied with excess air for cooling the chamber walls and for protection of the turbine nozzle and blading. Extremely high speeds of rotating compressors and turbines, up to 70,000 rpm for small engines, pose a potential hazard and require protective shields in the plane of rotation. The main advantages are very light weight, complete combustion, and freedom from vibration. Disadvantages include slow starting, high fuel consumption unless expensive recuperators are employed, susceptibility to blade erosion and damage, giving degraded performance, and sensitivity to matching compressor flow to turbine capacity without stalling or surging flow in the compressor.
Other investigators have attempted to marry the multi-piston reciprocating engine with high-speed turbines in combinations ranging in form from turbo-charged engines that have been commonly accepted for forty years, to free-piston engines that have been used as the combustor for power turbine output drives. All of these attempts have sought to use the highly efficient but momentary and cyclic operation of the piston-cylinder combustion chamber.
Those knowledgeable in the art understand that to realize the full potential of the internal combustion engines for automotive vehicles, propeller-driven airplanes and stationary applications, a new generation of engines with reduced engine size, increased engine power-to-weight ratios, and decreased full and part-load specific fuel consumption will have to be developed. Such engines will be designed to improve vehicle performance and will ease the logistic problem of providing fuel for the ever-increasing number of engines required. Careful attention will have to be given to both the aerothermodynamics and the mechanical design concepts selected for such engines, coupled with effective value engineering, mantainability, and reliability in order to reduce their manufacturing, operating and maintenance costs.
To achieve such significant improvement in engine performance, it is necessary to provide for basic improvement in aerodynamic and thermodynamic efficiencies. The major parameters which influence performance in Brayton cycle engines are the compressor pressure ratio and expander-inlet gas temperature. Increasing the compressor pressure ratio provides a significant decrease in specific fuel consumption, while increasing expander-inlet gas temperature provides significant increases in specific power. Analysis of a regenerated simple-cycle engine shows that high expander-inlet gas temperature provides a significant increase in specific power. A moderate decrease in specific fuel consumption is also obtained with increasing expander-inlet temperature. At expander inlet gas temperature in the 2200.degree.-2600.degree. F. range, specific fuel consumption is optimized for a recuperated engine at a compressor pressure ratio of about 10:1. Analysis also shows that the part-load specific fuel consumption of such a new generation of engines will also be reduced by up to 50% over the simple cycle versions. Indications are that higher turbine-inlet gas temperature, higher compressor pressure ratio, and lighter-weight, high-effectiveness recuperator technology are required for the future high performance engines.
The building of such engines requires significant advances in existing technology utilization. Expander materials with sufficient strength at the high temperatures encounterd in advanced gas turbine engines are now available but under utilized in automotive applications. Moreover, high compressor pressure ratios which in aerodynamic compression engine are currently obtained only by incorporating a complex and costly number of compressor stages, can be readily achieved in a single stage using a rotary piston compressor. The size and weight of current gas turbine recuperators severly restricts their use in mobile applications. A measure of recuperation can be attained at little extra cost in the new engine described below.
Every study of new engine cycles or configurations indicates the desirability of high pressure ratios and high gas temperatures. A compact, lightweight recuperator is also desirable. Minimizing the number of engine component stages will certainly reduce cost. The ability to efficiently obtain high cycle pressure ratios with a single stage, and the availability of materials, and design and manufacturing techniques which will allow operation at high gas temperatures, are prerequisites for the design of future generations of engines regardless of the thermodynamic cycle utilized. The invention described below easily accomplishes a single-stage pressure ratio of 16:1 in a simple cycle configuration and 10:1 pressure ratio in a recuperated version.
No prior art is known which is material or pertinent to the invention of this application.